Traditional electrophotographic (EP) devices comprise laser scanning units having a spinning polygon mirror that directs a laser beam to a photoconductor, such as a drum, to create one or more scan lines of a latent to-be-printed image. This type of polygon mirror is typically driven by a scanner motor that is controlled to run at a predetermined scan rate. Thus, the scanning rate is set by the EP device itself.
Recently, however, it has been suggested that torsion oscillator or resonant galvanometer structures can replace the traditional spinning polygon mirror to create scan lines in both the forward and reverse directions (e.g., bi-directionally) and increase efficiency of the EP device. Because of their MEMS scale size and fabrication techniques, the structures are also fairly suggested to reduce the relative cost of manufacturing.
In an EP device that uses a torsion oscillator or resonant galvanometer structure as a component of its laser scanning unit, the device process speed must adapt to a scanning rate supplied by the laser scanning unit. This can be a result of a variety of factors. For example, it is known that differences in ambient conditions such as temperature, humidity, air pressure, altitude, etc. may affect the oscillation rate of the torsion oscillator or resonant galvanometer structure. As a result, different EP devices may operate at a slightly different scanning rate which is at least partially defined by the scanning rate of the laser scanning unit. This results in variations in scanning rate between EP devices, which may require differences in EP device process speed. Similarly, operating an EP device at a faster scanning rate may impact the darkness level of the printed image in comparison to operating the device at a slower scanning rate.
Accordingly, there exists a need in the art for techniques for achieving consistent darkness levels between different EP devices without affecting device process speed. Particularly, there is a need for compensating for scanning rate variations in resonant scanning EP devices to achieve a consistent image darkness level from device to device. Naturally, any improvements should further contemplate good engineering practices, such as relative inexpensiveness, stability, low complexity, ease of implementation, etc.